The term “cardboard packaging” usually designates packagings whereof 90 to 98 wt % are made up of cellulose materials. In addition to layers of cellulose materials, this type of packaging comprises metal layers or coatings, such as aluminum, or synthetic ones, associated with cellulose materials to form a composite surface material. These metal or synthetic materials make up, according to the terminology generally accepted in the profession, a “barrier material”, isolating the product stored inside the packaging from the outside environment, for example to prevent oxidation, drying, or with respect to pollutants. The synthetic layers or coatings can also play an essential role in sealing between two parts of the packaging during its manufacture; in that case, they are generally described as “reactivatable barrier material”.
The French patent application by the applicant published under number FR 2,986,514 describes a method for manufacturing a packaging made substantially from cardboard, comprising a tubular body made from one or more layers of cardboard material and a complex sealing structure, assembled to the tubular body tightly, said sealing structure comprising a cover cardboard and a security membrane. This method comprises the flat assembly of three materials in sheets or strips, namely:                a cellulose material coated with at least one reactivatable barrier material on its face oriented toward said security membrane, making up said cover cardboard;        a laminating piece arranged between said cover cardboard and said security membrane, with a shape conjugated to the shape of the opening of the tubular body, made from paper, or coated paper, on its face oriented toward said cover cardboard, a material having sealing properties with respect to said cover cardboard, and        a material forming said security membrane, made up of a paper coated with at least one reactivatable barrier material and the face of which not oriented toward said laminating piece can be peeled.        
Patent application FR 1,261,400 by the applicant describes a method for manufacturing packagings made up of a tubular body made from a cardboard material and a complex sealing structure comprising a cover cardboard and a security membrane, as well as a machine carrying out that method, comprising                supplying a sealing unit with preformed tubular bodies, two by two, and with sealing structures in the form of flats, two by two, each comprising a central part with a shape conjugated to the shape of the opening of the tubular bodies, surrounded by a peripheral part able to be folded down that is sufficient to tightly assemble the sealing structure with the inner lateral wall of the tubular body,        inserting pairs of sealing structures into a shaping tool and shaping them in form of a basin;        inserting, placing and sealing the entire folded down peripheral part of the basins in the tubular bodies using said shaping tool;        transferring, two by two, tubular bodies assembled to the sealing structures to a finishing unit,        pre-cutting the lateral wall of the tubular bodies and partially pre-cutting covers along a peripheral line,        at least one operation for finishing the end of the packaging bearing said sealing structure.        
The description of patent application FR 1,261,400 is incorporated into this text through this citation and by? reference.
Many materials can be considered to produce a security membrane: aluminum and sealing film(s), aluminum and sealing varnish, paper and aluminum and sealing film(s), barrier film paper (e.g., metalized PET, PET SIOX, PVDC, etc.) and sealing film(s). The materials used must be compatible for sealing with the inner wall of the tube. If a complex with paper is used, the membrane can be printed and identified by spots in order to be caught and positioned perfectly centered in the tube.
With a known technique called “recess membrane”, the cut surface of the membrane is clearly much larger than the transverse surface of a given tube. During the passage from the flat state to the shaped state, folds are generated that constitute a proportionate number of wells that allow air and moisture to pass and therefore prevent good sealing of the assembly. To offset this, in the state of the art, it is necessary to use very strong materials in order to use very high pressure hold-down members, generally hydraulic. The range of usable materials is then practically limited to only aluminum with varnish. This poses cost problems, since aluminum is an expensive material, subject to considerable price variations. Furthermore, a large amount of material is necessary to perform this shaping operation, and it is therefore disadvantageous in terms of material cost and final competitiveness. The first aim of the present invention is to offer a method making it possible to use a wide range of materials to produce the security membrane.
Furthermore, in order to have easy opening, the sealing of the membrane on the tube must be easily “strippable”. To that end, in general in the state of the art, an attached tongue is used fastened to the periphery of the security membrane. Here again, this limits the choice of materials both for the membrane and for the barrier of the tube itself. Here again, the material costs are not optimized. The present invention also aims to produce a membrane allowing easy and reliable opening without being restricted in the choice of materials, as in the case of the methods of the state of the art mentioned above. The invention proposes to facilitate the separation of the security membrane during the first use, while decreasing the necessary pulling force, without, however, altering the tightness of the membrane before that first use.
The French patent published under no. FR 2,716,408 describes the manufacture of a tubular packaging of the above type. The structure comprises a cover cardboard made from a cellulose material and a security membrane made from a cellulose material coated with a barrier material. These two pieces are shaped one after the other, in the form of cylindrical basins using a shaping punch through an outer die and engaged in one end of the tubular body. The lateral walls of the two pieces are tightly assembled with the inner wall of the tubular body. Then, the wall of the tubular body is precut along a peripheral line situated between the assembly zones of the two pieces, so as to allow the opening of the cover cardboard without tearing the security membrane. The drawback of this method, specifically adapted to the assembly of cellulose/cardboard materials, is its inapplicability to a wide range of materials. The present invention also aims to offset this problem. The invention also aims to produce a structure comprising a tubular body as mentioned above, provided with a security membrane, on which structure it is possible to form and/or adapt a wide range of types of covers.